In removing residual monomer from aqueous polymer dispersions, following the polymerization process, severe foaming problems occur, especially during vacuum treatment. These foam layers, such as are formed, in particular, on vacuum treatment with simultaneous blowing in of steam, inhibit the unhindered passage of the stripping gas, and the material transfer from the dispersion into the gas space (volatilization of residual monomers), and hence altogether interfere with the success of effective removal of residual monomer from the polymerization batch. The toxicity of some monomers such as, for example, vinyl chloride, having been recognized, great value is attached to low residual monomer contents in polymerization products. Hitherto, attempts have been made to solve the foam problem by chemical anti-foam agents and by mechanical devices for combating foam. A process for blowing steam into the foam layer also did not give sufficiently satisfactory results.